DFT Studies On The Carboxylation And The Copolymerizatioin Of Epoxide With Carbon Dioxide

Carbon dioxide is an abundant, cheap, non-toxic, non-flammable, and easily available Cl resource. During the past several decades, carbon dioxide was widely used as carbon resource to prepare various organic molecules and polymers. Due to the chemical inertness of CO2, it is necessary for the CO2 reation to use transition-metal catalysts to ensure its effective transformation. Therefore, the development of highly efficient catalyst systems for CO2 reation has gained much attention of chemists. DFT theoretical calculation, which interprets the elementary reactions from molecular and electronic level, is a powerful tool in the study of reaction mechanism. The insight of reaction mechanism using DFT studies can help the researcher to design more excellent catalyst systems. Also, theoretical calculations can predict the effect of a new catalyst, reducing the intensity of the experiments greatly. The present thesis focused on the DFT theoretical calculation studies of the reaction mechanism involving the carbon dioxide as a reactant in detail, and expectantly designing more excellent catalytic systems. The main contents are as follows:1) A detailed study of the carboxylation mechanism of the reaction of terminal alkyne with carbon dioxide catalyzed by a ligand-free silver catalyst was performed, particularly exploring the role of the organic ligand and the effects of different bases. DFT calculations on the Ag-catalyzed carboxylation of phenyl acetylene with CO2 indicate that the true catalytically active species is a CsCO3--coordinated Ag complex rather than neutral PhC=CAg conventionally considered for such a process. The reagent Cs2CO3 not only functions as a base to abstract hydrogen from the substrate PhC?CH, as conventionally considered, but also plays a crucial role in formation of the catalytically active species in such a carboxylation process.2) A reaction mechanism of the carboxylation of phenylboronic esters with carbon dioxide catalyzed by the silver salt was studied, with a focus on the roles of the base and the organic ligand in this reaction. Compared with KO'Bu as a base, CsF or K2CO3 as a base showed much disadvantage in the thermodynamic and kinetics of the reaction. In the absence of organic ligands, the energy barrier of CO2 insertion process is higher than the energy barrier in the presence of organic ligands.3) A detailed DFT study on the difference in regioselectivity for the copolymerization reactions of styrene oxide vs. propylene oxide with CO2 utilizing binary SalenCo(?) catalyst systems was performed. This study focuses on the discrepancy of regioselective ring-opening of two terminal epoxides during the copolymerization with CO2. It was found that the nucleophilic ring-opening of styrene oxide occurred predominantly at the methine Co-O bond due to the election delocalization of phenyl group to stabilize the transition state for the methine C-O bond cleavage.4) The regioselective study was carried out for the desymmetrization copolymerization of CO2 and meso-epoxides using bimetallic cobalt complex as catalyst. Furthermore, the exploration of the driving force for cocrystallization of polycarbonates stereocomplexes was present. The results show that different chiral polycarbonate chains form many pairs of hydrogen bonds, when a carbonate unit of one enantiomer chain interacts with that of the opposite enantiomer chain, the adjacent carbonate unit will interact with a carbonate unit of the other opposite enantiomer chain, so the layer shape was the main structure for the stereocomplexed polycarbonates.